Coking retort oven firing method



June 1965 J. VAN ACKEREN ETAL 3,192,127

COKING RETORT OVEN FIRING METHOD 2 Sheets-Sheet 1 Fi1 ed April 13. 1961 SECTION 1-1 -$CTION l "l BLAST EFUENAGL GAS J. VAN ACKEREN ETAL 3,192,127

COKING RETORT OVEN FIRING METHOD June 29, 1965 2 Sheets-Sheet 2 Filed April 13. 1961 INVENTORSI' United States Patent 3,192,127 'COKING RETORT OVEN FWNG METHOD Joseph van Aelrercn and Edward J. Helm, Pittsburgh, Pa, assignors to Koppers Company, Inc, a corporation of Delaware Filed Apr. 13, 1961,8er. No. 102,868 7 Claims. (Cl. 2tl212) This invention relates to impnovements in the general operation of regenerative horizontal coking retort ovens, and more particularly, to a method of supplying fuel gas to high burners on every reversal of the .ovens in vertical heating lines of the heating walls of said ovens, by means of the heat of combustion of rich fuel gas without clogging the riser passages below the high burners, as a result of cracking and carbon deposition of constituents in the fuel gas in the riser passages to the elevated burners while flowing therethrough, by reason [of the fiow of combustion heat alongside the high burner riser passages from other burners in heating flues of the heating walls at lower elevation than the high burners.

In the normal operation of such ovens, when fired by rich fuel gas, it has been found that the amount of carbon formed by thermal decomposition of the coke oven gas fed through the low burner riser channels, during their on period of operation in the regenerative heating cycle, does not accumulated to a degree which decreases to any substantial extent the normal rate of flow to the low burners, provided the burners are decarbonized with air during the off period in the regenerative cycle. In the case of the high burners, however, it has been found that, due to the heat from the low burners, the high burner riser channels gradually accumulate such carbon to a much greater degree so that a substantial deleterious decrease in the normal rate of flow of gas occurs in the high burner risers in each on period of operation in the regenerative cycle, notwithstanding the high burners, like the low burners, are decarbonized in each off period in the regenerative cycle.

The principal purpose of the method of this invention is to provide a workable method of controllably supplying supplemental heat to the upper portion of the vertical heating fines of coke ovens in a manner which will overcome the objections to the prior methods which have been disclosed and/or tried up to now. A satisfactory method of providing such supplemental heat at a higher elevation is particularly important in order .to'assure the satisfactory operation and uniform vertical heating of ovens of relatively great height. The importance is further accentuated when relatively high ovens are heated entirely, or principally, with rich gas.

More particularly, the method involves the novel characteristic of supplying to high burners located in vertical flues on every reversal of the oven with a fuel gas mixture rich enough in heating value to supply the necessary additional heat at a high enough flame temperature to be sharply effective, and of such chemical composition that cracking and carbon deposition will not interfere with the proper operation of such burners. The composition and quantity of heat units in the fuel gas mixture delivered to the high burners are separately controllable to permit the utmost flexibility of regulation of vertical heat distribution, while maintaining control of the tendency of the gas to crack and deposit carbon. To provide the required control, it is essential that separate control of the quantity of heat units supplied, and of the chemical composition of the gas delivered to the high burners, be provided on every reversal of the ovens.

The quantity of heat units supplied to the high burners is controlled by regulating the total flow of fuel gasses supplied externally of the battery. This flow of fuel gas "ice may consist of a mixture externally of the battery entirely and at least in part of rich gasand lean gas or rich gas and inert gas.

The composition of the fuel gas delivered to the high burners is controlled within the necessary range to prevent excessive carbon deposition either (1) by controlling the ratio of rich and lean fuel gasses mixed externally to the battery, or (2) by controlling the ratio of rich fuel gas and inert gas mixed externally to the battery, or (3) by controlling in part the ratio of rich fuel gas and products of combustion mixed internally of the battery by waste gas recirculation before delivery .to the high burners, or (4) by a combination of two or all three of the above methods.

Broadly, the method of the invention consists essentially of internally controllably supplying a heating gas mixture which requires no regenerative preheating and the major portion of whose heating value is derived from 500 Btu. per cu. ft. coke oven gas or other still richer gas, to burners at elevations above the base of the vertical fines of coke ovens, and controlling the chemical composition of such rich-gas-containing mixture by means of an external mixture of low heat value gas chosen to prevent excessive cracking and carbon deposition in the risers to the elevated burners, while concurrently supplying heating gas from a separately controllable source to burners located at a lower elevation in the vertical iiues. The gas delivered to the burners at the lower elevation may be any suitable fuel gas such as blast furnace gas, coke oven gas, natural gas, etc., or mixture thereof. 1f blast furnace gas or other lean gas is supplied to the lower burners, it should be preheated in the regenerators. Rich gas may be supplied to the lower burners by either the gas gun system or the underjet system. Provision of waste gas recirculation for lower burners may be omitted or provided. Any of the conventional oven heating flue systems may be used but it is preferred to use hair-pin or cross-oven :flues or any similar type that are p-racticably adapted to waste-gas recirculation, because the method of the invention can be more flexibly employed when wasteas recirculation is in a part of the heating system.

The range of heating value of the final gas mixture as delivered to the high burners is approximately to 350 B.t.u. per cubic foot of gas mixture. The lower limit of the range is chosen because a still lower heat value will result in very limited useful heat input to the top portion of the tines because of low 1 tame temperature caused by excessive quantities of poorly preheated lean gases. The higher limit of the range is chosen because a still higher heat value will permit excessive cracking of .the rich gas With attendant carbon deposition.

in the accompanying drawings forming part of this specification, there is shown, for purposes of exemplification, the best mode of practicing the method of this invention in conjunction with a crossover flue interconnected combustion flue heating system in a coking retort oven battery, as described in the common assignees copending application Serial No. 102,791, filed April 1-3, 1961, now Patent 3,123,540 of Joseph van Ackeren, filed concurrently herewith, for Coking Retort Ovens. The said method while effective in heating systems having high and low burners in separate lines is especially eifective in the system of the said copending application wherein high and low burners are in the same fine and whereby there are avoided cool spots on the oven-wall, which would otherwise occur where the burners are so vertically separated .as to provide effective heating of tall ovens.

The method of the invention, however, is not limited in its application to this system but is equally applicable, as aforesaid, to the twin or hair-pin flue system, as well as other heating systems, such as the double divided heating flue system.

FIGURE 1 is a diagrammatic vertical section, the lines 1-1 being through the high burner riser passages and the lines 1a1a being taken through the low burners, of a battery of the well-known Becker underjet type of coke ovens of Patent No. 1,374,546, wherein there is embodied the features above set forth of separate riser channels of the present invention in conjunction with the van Ackeren Patent No. 2,306,678 waste gas recycling system for admixing a combustion medium in advance of its delivery into both high and low burners in each of the flame flues, with waste gaseous combustion products from corresponding combustion products flues of the battery, together with separate headers and mains for the riser channels to the high and low burners;

FIGURE 2 is an enlarged view of a fraction of FIG- URE 1 showing in greater detail the regulatory devices for delivering calibrated quantities of coke oven fuel gas into the riser channels in relation to the waste gas recirculating ducts in the underjet coke oven heating systems;

FIGURE 3 is a vertical cross-sectional View to illustrate the system as shown in FIGURE 1, but modified to have the recirculation ducts connected only to the high burners and their riser channels, and not to the low burners.

In this systemthe heating flues and regenerators are interconnected for gas flow by crossover flues 6 for on and off operation in two sets operable in alternation with each other for inflow of combustion media and outflow of waste gases of combustion.

The coke oven battery comprises a plurality of coking chambers 2 and heating walls 3 that are disposed in alternation lengthwise of the battery. The heating walls 3 are constituted of a row of vertical flame or combustion heating flues 4 that are disposed side-by-side crosswise of the. battery, and are grouped for gas flow purposes in flow groups of several heating flues 4 having a common cross-, over duct 6, whereby combustion products of each such group flow upward and over across the top of a coking chamber 2 into a corresponding flow group adjacent the opposite side of an intermediate coking chamber. Each flow group of fluesv 4 is provided with a common horizontal flue ,7 and the flues of a flow group usually are symmetrically disposed in respect of its crossover duct 6.

The heating flues. 4 of the heating walls each communicate individually by regenerator port and duct assemblies 8 with two cross-regenerators 9 therebeneath, each such regenerator being arranged to preheat combustion air at such times as the heating flues are being underfired with rich fuelgas as, for example, obtains when the ovens of the battery are underfired primarily with coke oven gas. One of the regenerators of the pair of regenerators with which each heating flue 4 is communicably connected, is also adapted to preheat lean fuel gas delivered thereto from a lean fuel gas main gas flow box (not shown) to an inlet at one side of the battery to the sole channels 11 in a Well-known manner, in those instances, where the ovens are operated as gas ovens and are, therefore, underfired with extraneously derived lean gas, such as blast furnace or producer gas. In the underfiring of the heating flues with'regeneratively preheated lean fuel gas, the lean fuel gas, as well as the combustion air, are all introduced at one level in the lower parts of the heating flues 4.

When the battery is heated by rich'fuel gas of higher calorific value that needs no preheating step for effecting coking beat, this rich gas is delivered into the bottom of the heating flues 4 in accordance with the underjet principle by means of separate low burner and high burner rich gas riser channels 13, 15 that extend from the lower surface of the supporting mat 14 of the battery upwards through regenerator walls 16 to port into the lower half parts of the heating flues 4. As can-be seen from the drawings, each riser channel 13 leads to a low gas burner port 18, and each riser channel 15 leads to a high burner port 17 through its associated riser extensions 15. It is to be understood that control nozzles (not shown) that usually are provided in a known manner at each of the ports 17 and 18 to apportion the amount of gas to be delivered into the flues 4 from each of such ports, are to be omitted. Each low burner riser channel 13 for all lines 4 in a heating wall, communicates by means of underjet duct pipe connections 26, with a header pipe 19 below the mat 14, and each high burner riser channel 15 for each flue 4 likewise communicates, by means of underjet duct pipe connection 26a, to a separate header pipe 1%, whereby all the heating flues 4 in a single heating wall are simultaneously supplied with the rich coke oven heating gas of high calorific value from one side of the battery. Each such wall header pipe 19., 19a of the battery also communicates, in accordance with the present invention, through individual pipe connections 20, 21 with a separate principal supply main 22,. 2.2a that extends lengthwise along the side of the battery and communicates through gas main 39 with a reservoir of rich coke oven gas from the battery (not shown). Valve and ga s flow reversing mechanism 23 is provided to supply fuel gas to each heating wall in alternation with an associated heating wall there adjacent. In a manner similar to that disclosed in the above-rnentioned Patent No. 2,306,678, the two sets of underjet riser channels 13, 15 that are each associated with corresponding on and off heating flues of adjacent heating Walls employing the same crossover duct 6, are communicably connected adjacent their lower ends by means of a waste gas recirculation induction duct 24 located in mat 14 or in the brickwork under the sole flues. This waste gas recirculation duct provides means, whereby a circulation of waste combustion gases is established between the downflow vertical flues and the upflow risers to the high and low burners for the upflow heating flues connected thereby. The recirculation duct 24 can be arranged with respect to the mat in one of a number of ways as set forth in the aboveanentioned patent. Preferably, it is arranged as shown in accordance withithe invention as described in the common assignees copending application of Linwood G. Tucker Jr., Serial No. 622,l70,'filed November 14, 1956, entitled Recirculating Underjet Coking Retort Oven, now Patent No. 3,047,474.

Fuel gas, such as coke oven gas, contained under pressure in the separate header pipes 19, 19a of the distributive system. is' allocated individually to low and high risers, 13, 15, for each heating flue of an associated heating wall by means of the separate underjet duct branch pipe connections 26, 26a, each branch pipe having a calibrated orifice tip nozzle 27 in its outlet end for removable insertion of the removable tip and nozzle into the lower part of its recirculation duct 24 and in alignment with an underjet riser duct 13 or 15. The rate at which fuel gas is delivered to the individual underjet riser channels 13, 15, is controlled by means of the gas flow orifice nozzle arrangement 27 cooperating with the branch pipes 26, 26a. These nozzles are withdrawable downwardly through the pipes 26, 260. By variation in size of the orifice tip in the nozzle 27 and by variations in the gaseous pressure maintained in the header pipes 19, 1911, the amount of waste gas and or fuel gas separately delivered to the high and lower burner ports 17, 13 for each heating flue, can likewise be varied.

By means of the above-described fuel gas system, fuel gas individually injected into the underjet riser channels 13, 15, causes Waste gases of combustion to flow downwardly from an o flame line 4 through its idle burners 17, 18, and their riser channels 15, 13, to the recirculation duct 24, and thence, adrnix with the rich gas as a diluent to enter the burners 17, 18, for the on combustion flues 4. In the heating flues temperatures in the range of 2600 F. are developed and coking in the coking chambers is completed in an average coking time in the range of seventeen hours. Due to the flow of part of the waste gases down through the riser channels 15, 13 the brickwork is heated thereby and rich gas rising therev the coke oven gas in the main 2.2a.

through can be preheated to the range of 1800 F. or higher.

Inasmuch as these combustion products are relatively inert, containing N CO H 0, and a little 0 their mixing with the rich fuel gas as they rise through the underjet riser channels, has the effect of introducing into the low gas burner 18 and the high gas burner port 17 thereabove of the heating lines 4, when operable for upflow, a diluted rich fuel gas of lower calorific value and of slower combustion characteristics than would otherwise obtain with the rich fuel gas alone. This not only has the beneficial eifect of making it possible to maintain a reduced temperature gradient between the tops and bottoms of the heating flues 4 to promote uniformity of heat distribution throughout the adjacent coal charge in the intervening coking chambers 2, but in addition, has the effect of preventing the greater .and more rapid formation of carbon that is frequently deposited in the riser and riser extensions 15', of the high gas burners 17, and which would otherwise take place therein to a greater extent than in the risers 13 for the lower burners 18, through the cracking of the undiluted rich fuel gases but is great- 1y reduced by means of the individual dilution of the rich gases for the high burner risers 15 with the waste gases from the recirculating ducts 24.

The coke oven gas fed by line 22a to the underjet duct riser channels 15 for the high burner ports 17, may feed the gas at .a higher pressure through the orifices 27 in the connections 25a, than the pressure at which the line 22 feeds coke oven gas .to the orifices 2.7 in the connections 26 to the underjet duct riser channels 13 for the lower burner ports 18. This is done to provide a greater velocity of flow through the jet at the venturi 24' to cause .a greater portion of Waste gas to be aspirated through the recirculation ducts 24 and the riser channels 15 to the high burners 17, rather than the same amounts as might flow through the lines 13 for the lower burners 18, in order to achieve more dilution of the fuel gas and a greater amount of reaction of CO and H 0 with carbon to prevent it from forming faster and in greater amounts, in the high burner riser channels 15 than in the low burner riser channels 13 in each twenty to thirty minute period of onfiow operation of these lines in the regenerative cycle.

With this novel method, to attain a still greater dilu tion for the high burner riser passages l5, l5 lean gas, such as blast furnace gas from line 28 may be mixed with This'blast furnace gas is denser than coke oven gas and contains much larger amounts of N and CO Such denser gas in-mixture with the coke oven gas, acts, as the mixture of gas emerges from the calibrated orifices in the tip of the nozzle 27, to induce a larger portion of waste gas to be aspirated through the recirculation ducts 2-4 into venturi 24' of the high burner lines 15, than the undiluted coke oven gas does for the low burner lines 13. This blast furnace gas also provides on every reversal, or on period of operation, a further quantity of diluent gas in addition to the greater portion of the waste gas obtained from the recirculation ducts as a dilution gas, since the blast furnace gas contains a very large quantity of N and CO2.

Valves29 in the mains 22., 22a, at a region remote from the oven battery, separately control the flow to all of the high 17 and low 18 burners of the battery from a single region. More or less gas can be fed to the high burners or the low burners by manipulation of these valves. When desired, all the high burners 17 may be cut off from operation by completely closing the valve 29 in the line 22a, so that only the low burners are used for underfiring the battery.

When it is desired to underfire the battery solely by means of regeneratively preheated lean gas, instead of rich gas, then both valves 29 are completely closed, thus shutting off .the lines 22, 22a from the source 30 of coke oven gas, and the supply of blast furnace gas is also cut off from line 22a by means of its valve 31. In such case, one-half of the regenerators operate in alternation for inflow of lean gas, in one of a pair, and air in the other of each pair of regenerators, for lean-s gas underfiring of the battery.

Referring to FIGURE 3, the apparatus as thus devised is for high burner operation without plugging of the high burner riser channel extension 15 in coking retort ovens in which the structure is equipped for waste gas recirculation only to the high burners. In such case, the apparatus is the same as above described in FIGURES 1 and 2, except the riser channels 13 for the low burners 18 are not equipped with the venturi aspirators 24'; nor otherwise connected up to the recirculation ducts 24. Only the rich gas risers 15 for the high burners 17 communicate with the recirculation ducts 24 through the venturi aspirators 24'. The low burner rich gas riser chan nels 13 are, instead, formed of straight sides all the way down to the jet nozzles 27 and are decarbonized with atmospheric air during the off period of these risers 13.

Otherwise, the operation is the same as disclosed in connection with FIGURES 1 and 2, the difference being that lean gas such as blast furnace gas may be mixed by line 28 with the rich gas in line 22a on every reversal to produce, in conjunction with the waste gas from ducts 24, the desired heating value between 170 and 350 Btu. per cu. ft. as the total or final gas mixture delivered by the high burners 17, whereas the low burner rich gas is not diluted by either the wastev gas from ducts 24 or by blast furnace gas.

In accordance with the invention of the present method,

if the total amount of dilution gas supplied external-1y of the battery in the form of inert gas or low heat value gas containing N and CO such as blast furnace gas, supplied by line 28 and mixed with the straight rich gas, in line 22a, is not suflicient to reduce the heat value of the total gas mixture to a Btu. value between 170 and 350 per cu. ft., then some internal dilution with products of combustion by waste gas recirculation must be provided to deliver to the high burners a total mixed gas of composition that will not cause excessive cracking and carbon deposition. When rich gas is mixed with either lean gas or inert gas by line 28 external to the battery, additional internal dilution with products of combustion by duct 24 may or may not be required depending upon the composition of the mixture supplied externally. Obviously if internal dilution with recirculated waste gas is provided, less external dilution of the rich gas with either lean gas or inert gas will be required to obtain a final gas composition in the risers to the high burners that will prevent excessive cracking and carbon deposition. However, it is possible to control the composition entirely by external blending with blast furnace gas and/or dilution with waste combustion products gas or other inert gas, without any internal waste gas recirculation, and retain complete control oi. both the quantity of heat units supplied and the chemical composition of the gas. The following examples illustrate the various B.t.u. values between 170 and 350 B.t.u. per cubic foot that may readily be attained, in accordance with the invention, when underfiring the high burners of coke ovens with rich and lean gases having the following properties:

B.t.u. per Sp. Gr.

cu (Air=1.0)

Coke Oven Gas 530 0. 40 Blast Furnace Gas 1.01 Products of Combustion 0 1.0

- with them as they flow through the venturi 24'.

ously being delivered through the'lovr burner risersand burned in the heating flues alongside the riser extension to the high humor in the fines, coke oven gas is fed from the rich fuel gas main 30 simultaneously in supply mains 22, 22a for delivery through pipe connections 20, 21 to the principal supply mains 22, 22a, for alternate ones of heating walls 3. At the same time blast furnace gas is fed from gas main 28 into the supply main 22a for all of the high burners 17. The valve 29 in line 22a is set to deliver coke oven gas as 95% of the total amount of gas in the after part of the line 22a, and the valve 31 is set to deliver blast furnace gas as of the total amount of gas in the after part of line 22a. The mains 22, 22a then discharge their streams of gas separately and simultaneously through branches 26, 26a and their nozzles 27 in calibrated amounts into the lower ends of the separate riser channels 13, leading respectively to the low 18 and high 17 burners in the same vertical combustion fines 4 in the alternate heating walls. As seen in FIGURES l and 2, the separate streams of fuel gas induce a flow of waste gas into mixture About 1.0 volume of recirculated Waste gas is induced into each stream per volume of gas issuing from the nozzles 27. The B.t.u. of the mixture as it passes the throat 24 in the high riser passage 15 is about 242 B.t.u. per cubic foot, since the volume of 95 coke oven gas and 5% lean gas from the lines 22a, 21, 26a and nozzle 27 when mixed with the equal volume of waste gas from the recirculation duct 24, produces a composition of that 242 B.t.u. per cubic foot with a specific gravity of about .71. This fuel gas mixture of about 240 B.t.u. per cubic foot is burned in the fines 4 by combustion with air preheated in the regenerators 9, which air flows to the bases of the fiues through the regenerator ducts 8. This air is preheated as a result of absorption of heat from the contact mass in the r-egenerators 9, 9, during flow of the air inwardly through the sole fiues 11 and upwardly in the regenerators 9, 9, to the ducts 8. The gases of combustion flow upwardly in the flues 4 to the crossover fiues 6, which deliver the burnt gases downwardly into the tops of the heating flues 4 in the intermediate heating walls 3. The gaseous combustion products flow downwardly in these heating lines 4 to the bottom thereof, where they are drawn off from the heating walls 3 through the regenerator ducts 8 at .the base of the the tops 17 of the riser extensions 15' and pass down through the riser passages 13, 15, to the waste gas recirculation duct 24, which intercommunicably connects the riser passages 13, 15 of the intermediate heating walls 3 with the corresponding riser passages 13, 15 in the alternate Walls 3.

This flow of part of the Waste gas from the downflow fines 4 downwardly through the riser passages 13, 15 and thence into the recirculation ducts 24, is induced by the injector effect of the entering fuel gas in the risers 13, 15 for the alternate heating walls 3, as a result of the venturi 24 located within the riser passages 13, 15 just above the.

nozzle 24. After about 25 to minutes, the direction of These ducts 8 discharge the waste flow is reversed, as by operation of valves 23, so that fuel gas and air now flows through the aforesaid air and gas elements for the intermediate heating walls 3, and the waste gases flow downwardly and out through riser passages 13, 1S and regenerators 9 for the alternate heating walls 3.

(2) To deliver to the high burners 17 a rich gas mixture having a heating value of about 170 B.t.u. per cubic foot at a specific gravity of about .80 without carbon accumulation in the high burner risers 15, 15', to a degreewhich would decrease to any substantial extent the normal rate of flow thereto, with recirculation of waste gas into the mixture, the same procedure as employed as above described in Example 1 is used, except that the valves 29 and 31 in lines 22a and 20 are adjusted to deliver to the afterpart of line 22a, 60% colqe oven gas from the rich gas main 30 and 40% blast furnace gas from the blast furnace gas line 28. With this proportion of blast furnace gas in mixture with that amount of coke oven gas, the gas from line 22a induces a recirculation of waste gas into the high riser passages 15, 15' in amounts of about 1.1 volume of recirculated waste gas per volume of the mixture of coke oven and blast furnace gas. This produces a fuel gas mixture of about 170 B.t.u. per cubic foot and a specific gravity of about .80. i

(3) To deliver without carbon accumulation in the high burner risers 15, 15 to a degree which would decrease substantially the normal rate of flow of fuel thereto, a gas mixture having a heating value of about 350 B.t.u. per cubic foot and a specific gravity of about .65 in the high burners without recirculation of waste gas, the same procedure is employed as above described in Example 2, except that the recirculation ducts 24 are omitted from the coke oven heating flue system, or are blocked off by the incorporation of shut off valves (not shown) in the recirculation duct line 24. In such case, the valves 29 and 31 in lines 22:: and 28 are adjusted to deliver to the afterpart of line 22a, 60% coke oven gas and 40% blast furnace gas. The B.t.u. of this mixture is about 354 B.t.u. per cubic foot and the specific gravity is about .64.

Any other intermediate B.t.u. value can be obtained, between 170 and 350 B.t.u. per cubic foot, by other simple adjustments of the valves 29 and 31 to alter the proportions, of coke oven and blast furnace gas or inert gas when carrying out the method according to Examples 1, 2 and 3 above. This may be illustrated by the following further example.

(4) If it is desired to deliver coke oven gas at a B.t.u. value of 244 B.t.u. per cubic foot without waste gas recirculation in the oven battery system, this is readily attained by adjusting the valves 29 and 31 to deliver to the high burners without Waste gas recirculation, by the procedure as set forth in Example 3. This is accomplished by closing a valve (not shown) in the recirculation ducts 24, or by employing the coke oven apparatus as above described but devoid of equipment for recirculating Waste gas within the boundaries of the oven battery. When this is done, the B.t.u. of the mixture is about 244 B.t.u. per cubic foot, and of the heat value would be provided by the coke oven gas and 25% by the blast furnace gas. In this case, if 50% of the total heat value of all the fuel gas for the heating flue is fed through the high burners, the heat value of the unpreheated blast furnace gas. would represent only about 12.5% of the total heat value of the fuel for the heating fiue. If only 25 of the heat value of all the fuel gas is fed through the high burners, the heat value of the unpreheated blast furnace gas would represent only about 6.25% of the total heat value of the fuel for the heating flue. In any case, although the blast furnace gas fed to the high burners does not pass through the regenerators, it will be partially preheated by contact with the hotbrickwork of the risers to the high burners.

The novel method of the invention also lends itself to being employed for the improved high burner operation of the heating fiues, for instance, in accordance with any or all of the foregoing four examples, but without having any waste gas recirculation at all for the low burners. This may be readily seen from FIGURE 3 of the drawings. As thereshown, the recirculation duct 24 is connected only with the high burners 17 through their riser passages 15,15. The duct 24 is not connected with low burners 13, nor with their riser channels 13. Only the high burner riser channels 15 are provided with the venturi 24'. In such case decarbonizing air infiltrates into the low burner riser passages 13 from theouter atmosphere through a small perforation (not shown) in the removable cap 27' at the base of the connection 26. This cap 27 is conventional in ovens of this type for access in removing and replacing the calibrated orifice tips 27. When waste gas recirculation is not relied on for maintaining these riser passages clear of carbon deposits in the risers, these caps 27' are conventionally perforated ones for infiltration of decarbonizing air.

To carry out the method of the invention in a battery as shown in FIGURE 3 of the drawings, the same procedure may be employed as above described in Examples 1 to 4.

Thus, the fuel gases can be premixed in the range of 5 to 40 percent lean gas, such as blast furnace gas with 95 to 60 percent rich gas, such as coke oven gas, and with the addition of waste gas quantities in the range of 0 to 150 percent of the coke oven gas in the mixture. The method of the invention lends itself to use in a variety of ways of adjusting the ratio of rich fuel gas of lesser density to lean gas of greater density so as to maintain a final fuel gas composition between 170 and 350 B.t.u. and to aspirate between 50 and 150 percent waste gas in ratio to the rich coke oven gas.

Although, as stated above, internal recirculation of waste gas for admixture by duct 24 with the fuel gas supplied to the high burners by line 22a is not necessary always for satisfactory operation of the method disclosed herein, there are certain advantages of combining external mixing of rich and lean fuel gas containing N and C0 with internal mixing with recirculated waste gas containing N H 0, and C0 The water vapor and CO content of recirculated Waste gas are especially advantageous in suppressing the tendency for carbon deposition. The sensible heat content of the hot recirculated waste gas is also advantageous in maintaining a high flame temperature. External mixing of rich and lean gas containing N and CO provides for controlling the heat value and composition of the final mixture supplied to the high burners, after mixing with recirculated waste gas, over a much wider range than could be attained by providing only internal mixing of rich fuel gas with recirculated waste gas, without external mixing with lean gas. External mixing with lean gas as aforesaid provides a two-edged means of control of final composition on every reversal by (1) its effect on the composition of the external mixture fed to the battery and (2) by the effect on the ratio of recirculated waste gas caused by increasing the volume and specific gravity of the external gas mixture fed to the aspirating nozzle jets of the waste gas recirculating system. This increased volume and specific gravity of the motive gas fed to the aspirating jets provides the possibility of recirculating much more Waste gas than could be aspirated by rich gas alone, since the ratio of waste gas to motive gas that can be aspirated by a nozzle jet recirculation system has rather narrow limitations. All that has been said above refers only to the system for supplying and controlling the gas mixture to the high burners, irrespective of what system :or type of gas is supplied to the low burners, or of what type of heating flue system is used.

The application of this method to ovens of different designs includes, for example, its application to ovens with high and low burners in alternate flues as well as ovens with high and low burners in the same flues. The gas of controlled composition and heat value can be delivered on every reversal to the high burners without any waste gas recirculation, in ovens that do not have means for recirculation of waste gas as above described, by externally mixing lean gas or inert gas with rich gas and delivering it through a separate main and header system to the high burners while delivering solely rich gas to the low burners. The gas of controlled composition and heat value can also be attained by providing waste gas recirculation to both high and low burners using the same rich fuel gas from lines 22 and 22a in the jets for both the high burners and the low burners in conjunction with premixing in line 22a of low heat value gas from line 28 with rich gas from line 30, but obtaining a higher degree of recirculation in the high burners by delivering the gas to the jets for the high burners at a higher pressure than for the low burners. Still another way would be to deliver a gas of relatively low B.t.u., obtained by external mixing, to the high burners, in addition to waste gas recirculation in the high burners. This last way can be incorporated either with or without waste gas recirculation for the low burners, and at the same or at different pressures. With any of the above-described examples, the gas supplied to the low burners might alternately be lean gas preheated in the regenerators instead of rich gas as described above.

The invention as hereinabove set forth is embodied in a particular form and manner but may be variously embodied within the scope of the following claims.

We claim:

1. A method for underfiring a regenerative coke oven battery by means of high and low burners in vertical flues alongside coking chambers, comprising the steps of:

(a) mixing externally of said coke oven battery a lean fuel gas having a low heating value with a rich fuel gas having a heating value of at least 500 B.t.u. per cubic foot to form a first portion of a final ga mixture for said high burners;

(b) mixing internally of said coke oven battery a quantity of said first gas with a quantity of gas including the waste products of combustion of said battery and forming said final gas mixture having a heating value Within the range of 170 to 350 B.t.u. per cubic foot of said final gas mixture; and

(c) delivering said final gas mixture to saidhigh burners while concurrently and separately delivering a fuel gas to said low burners.

2. A method for underfiring a regenerative coke oven battery by means of high and low burners in vertical fiues alongside coking chambers, comprising the steps of:

(a) flowing a final gas mixture to said high burners comprising a denser fuel gas having a low B.t.u. value and a rich fuel gas of lesser density and greater B.t.u. value mixed externally of said coke oven battery;

(b) separately delivering a fuel gas to said low burners;

and

(c) combining internally of said coke oven battery the externally mixed gases in aspirating relation with waste gases from said battery.

3. A method for underfiring a regenerative coke oven battery by means of high and low burners in vertical fiues alongside coking chambers, comprising the steps of:

(a) flowing a gaseous mixture to said high burners comprising a denser fuel gas having a low B.t.u. value and a rich fuel gas of lesser density and greater B.t.u. value mixed externally of said coke oven battery as a first portion which is combined internally of said battery in aspirating relation with waste gases from said battery forming a second portion and producing a final fuel mixture having a heating value within the range of 170 to 350 B.t.u. per cubic foot of final gas mixture, with the proportion of waste gases in said final mixture being present in amounts ranging up to percent of the rich gas fed through said high burners; and

(b) separately delivering a fuel gas to said low burners.

4. A method for underfiring a regenerative coke oven battery by means of high and low burners in vertical flues alongside coking chambers, comprising the steps of:

(a) flowing a gaseous mixture to said high burners comprising a denser fuel gas having a low B.t.u. value and a rich fuel gas of lesser density and greater B.t.u.

value mixed externally of said coke oven battery as a first portion which is combined internally of said battery in aspirating relation with Waste gases from said battery forming a second portion and producing a final fiuel mixture having a heating value Within the range of 170 to 350 B.t.u. per cubic foot of final gas mixture, withthe proportion of Waste gases in said final mixture being present in amounts ranging up to 150 percent of the rich gas fed through said high burners; and

(b) separately and concurrently delivering a fuel gas to said low burners.

5. In a coking retort oven including a plurality of 10W first burners and high second burners disposed above the level of said burners in heating fiues adjacent coking chambers, the method of underfiring said oven comprising the steps of:

(a) delivering to said high second burners a gaseous fuel'mixture including a first portion comprising a fuel gas having a calorific value of at least 500 B.t.u.

per cubic footot gas mixed externally of said battery with a fuel gas having a calorific value that is less than 500 Btu. per cubic foot of gas, and a second portion mixed with said first portion internally of said battery and comprising a gaseous substance derived from the products of combustion of said oven, said first and second portions being combined in such proportions that the calorific heating value of the final gaseous fuel mixture is Within the range of 170-350 B.t.u. per cubic foot of final gas mixture;

and

(b) delivering concurrently and separately to said'low first burners a quantity of gaseous-fuel.

6. A method as claimed in claim 1, and in Which the rich gas is mixed externally of the battery as aforesaid with lean gas as the gas of low heat value and in proportions of 60 to 95 percent rich gas to 40 to 5 percent lean gas.

'7. The method set forth in claim 5 wherein a (a) said first gas and said second gas are mixed together respectively in proportions Within the range of 60 to 95 percent of said first gas and 40 to 5 percent of said second gas; and

(b) said third gas is mixed With a quantity of said gaseous mixture in'amounts ranging up to 200 percent of the final gaseous mixture fed to the high burners; and (c) separately delivering a fuel gas to said low burners.

References Cited by the Examiner UNITED STATES PATENTS 2,306,366 12/42 Becker a 202-151 2,507,554 5/50 1 Van Ackeren 202--151 I I FOREIGN PATENTS 577,126 6/59 Canada.

MORRIS O. WOLK, Primary Examiner.

ALPHONSO D. SULLIVAN, DELBERT E, GANTZ,

Examiners. 

1. A METHOD FOR UNDERFIRING A REGENERATIVE COKE OVEN BATTERY BY MEANS OF HIGH AND LOW BURNERS IN VERTICAL FLUES ALONGSIDE COKING CHAMBERS, COMPRISING THE STEPS OF: (A) MIXING EXTERNALLY OF SAID COKE OVEN BATTERY A LEAN FUEL GAS HAVING A LOW HEATING VALUE WITH A RICH FUEL GAS HAVING A HEATING VALUE OF AT LEAST 500 B.T.U. PER CUBIC FOOT TO FORM A FIRST PORTION OF A FINAL GAS MIXTURE FOR SAID HIGH BURNERS; (B) MIXING INTERNALLY OF SAID COKE OVEN BATTERY A QUANTITY OF SAID FIRST GAS WITH A QUANTITY OF GAS INCLUDING THE WASTE PRODUCTS OF COMBUSTION OF SAID BATTERY AND FORMING SAID FINAL GAS MIXTURE HAVING A HEATING VALUE WITHIN THE RANGE OF 170 TO 350 B.T.U. PER CUBIC FOOT OF SAID FINAL GAS MIXTURE; AND (C) DELIVERING SAID FINAL GAS MIXTURE TO SAID HIGH BURNERS WHILE CONCURRENTLY AND SEPARATELY DELIVERING A FUEL GAS TO SAID LOW BURNERS. 